Method of manufacturing synthetic fibers of polyvinyl alcohol having good stable configuration and water solubility



United States Patent 3,383,447 METHOD OF MANUFACTURING SYNTHETIC FIBERS 0F POLYVINYL ALCOHOL HAV- ING GOOD STABLE CONFIGURATION AND WATER SOLUBILITY Shigekazu Onishi and Eiichi Morita, Okayama, Japan, assignors to Kuraslliki Rayon Company Limited, Kurashiki, Japan, a corporation of Japan No Drawing. Filed Apr. 10, 1964, Ser. No. 358,925 Claims priority, application Japan, Apr. 23, 1963, 38/20,843 3 Claims. (Cl. 264-205) ABSTRACT OF THE DISCLOSURE A process for the preparation of polyvinyl alcohol fibers having excellent dimensional stability and water solubility, comprising dry or semi-melt spinning an aqueous solution of polyvinyl alcohol having a concentration of greater than 30 percent by weight, adjusting the moisture content of the resultant fibers to a value between 50 and 120 percent by Weight, stretching said fibers to a ratio of from 1.1 to 3.0 at a temperature of from 0 C. to 100 C., drying such stretched fibers until the moisture content thereof is reduced to a value between 4 and 20 percent by weight, again stretching the said fibers to a ratio of from 2 to 6 at a temperature of less than 160 C., maintaining the said fibers at the constant length and strain imparted thereto by the latter stretch, and thence setting such strain. The resultant polyvinyl alcohol fibers are useful for base cloths in the manufacture of chemical laces.

The present invention relates to a method of manufacturing synthetic fibers of polyvinyl alcohol having good configuration stability and water solubility.

It has heretofore been well known to manufacture easily water soluble synthetic fibers of polyvinyl alcohol (hereinafter abridged as PVA) having the softening point of 7090 C. by dry spinning aqueous solution of PVA and by subjecting spun fibers, after dried, to the heat stretch under a high temperature of at least higher than 120 C. and heat setting at about 200 C.

The fabrics made of easily water soluble synthetic fibers of PVA used for the base cloth for chemical laces have disadvantage of causing excessive elongation and contraction or swelling affected by the change of temperature and moisture if PVA fibers of unstable configuration are used for weaving the fabric so that such fabrics are not desirable for the manufacture of laces since the dimension stability of the fabric is low. In order to avoid the above defects, contrivances have been tried to improve the dimension stability by selecting the heat setting condition to a higher temperature and longer duration in the process of manufacturing synthetic fibers of PVA. On the other hand, however, the water solubility becomes worse and in order to adjust such contradictory effects it was only one method of improving the PVA fibers to be used for the base fabric of chemical laces to properly regulate the condition of heat setting.

After numerous experiments and various investigations about the lower temperature stretch of synthetic fibers of PVA, the inventors have succeeded in producing synthetic fibers of PVA having excellent dimension stability and good water solubility by a method entirely different from heretofore usual methods.

According to the invention, it is characterized in that an aqueous solution of PVA having a higher concentration above 30% is spun by dry spinning or semi-melt spinning and the fiber thus obtained is subjected to a low temperature stretch under such conditions that the mois- 3,383,447 Patented May 14, 1968 ture content of the produced filament is 30-120%, preferably -90%, the ambient temperature at 0100 C., preferably nearabout room temperature, and the stretch ratio of 1.1-3.0, then drying the filament to moisture content of 420%, preferably about 10%, and subjecting it again to a low temperature stretch .of the stretch ratio of 2-6 times, preferably more or less 4 times, at a temperature "below the secondary transition temperature of 160 C., thereby forming a proper strain within the PVA filament, and then left under the constant length in order to set the strain and thus succeeded in the manufacture of synthetic fibers of PVA having excellent dimension stability and good water solubility by forming a suitable strain in the filament and by further setting the strain thus formed.

The low temperature stretch .of the first step is preferably performed at a temperature below C. for the purpose of preventing excessive coagulation of filament. At more than of moisture it is diflicult to provide uniform filament when stretched and at less than 50% it is substantially impossible to effect the second stage low temperature stretch so that it is not desirable for the purpose of improving the tenacity of the produced threads.

The stretch ratio higher than 3.0 is not desirable as it affects the second stage stretch and degrades the quality of products.

The second stage low temperature stretch at a temperature higher than C. considerably increases the crystallization of filament and consequently reduces the water solubility .of the produced threads and the moisture content of more than 20% reduces the solubility of the product, while at less than 4% the stretching becomes difiicult so that the tenacity of the produced thread is low and a suitable strain can not be produced within the filament and accordingly the solubility is not good. The stretch ratio of 2-6 times is most suitable, and at higher than 6 times crystallinity becomes better to decrease solubility, whilst at less than 2 times proper strain can not be produced in the filament, thereby spoiling the solubility.

In order to firmly set the strain formed in the filament after the low temperature stretch, it is preferable to wind the stretched filament around a bobbin to maintain the constant length and left for a long time in an atmosphere of room temperature.

The invention will now be explained more in detail by examples.

Example 1 A concentrated aqueous solution of PVA of 47% concentration having the average degree of polymerization of 1,700 was spun by means of a semi-melt spinning process and the filament thus obtained under the state of moisture content of 80% was stretched to 1.2 times at a lower temperature, then dried to the state of 10% moisture content and stretched at a low temperature of 100 C. to 4.0 times, then filament of 6.75 denier having strain therein was wound around a bobbin and left for 24 hours at a temperature of 20 C. and relative humidity of 65% to set the strain. Thus the PVA filament was obtained having dry tenacity 4.0 g./d., dry elongation 15%, and dissolving temperature in water 84 C., and also having good dimension stability and water solubility.

Example 2 An aqueous solution of PVA having the average degree of polymerization 1,700 and 43% concentration was spun by a dry spinning process and the filament thus obtained was stretched under the state of 90% moisture content to 1.2 times at a low temperature, then dried and reduced the moisture content to 12%, and subjected to the second heat stretch to 3.0 times at a low temperature of 100 C. The filament thus obtained having inner strain was taken up around a bobbin and left for 24 hours under the condition of temperature at 20 C. and relative humidity 65%, thereby providing PVA filament of 300 denier having dry tenacity of 2.5 g./d., dry elongation 19.0% and melting point in water of 82 C. and having good dimen sion stability and water solubility.

Example 3 A concentrated aqueous solution of PVA of 43% con centration having average degree of polymerization 1,200 was spun by a dry spinning process and the filament thus obtained was stretched under the state of 100% moisture content to 1.2 times, then dried to reduce the moisture content to and it was stretched again to 4.0 times at a low temperature of 100 C., thus the filament having inner strain was taken up around a bobbin and left for 24 hours at C. and 55% relative humidity.

Thus obtained PVA filament had 300 denier and showed dry tenacity of 3.0 g./d., dry elongation 10.0% melting point in water 73 C. and good dimension stability and water solubility.

What we claim is:

1. A process for the preparation of polyvinyl alcohol fibers having excellent dimensional stability and Water solubility, comprising dry spinning an aqueous solution of polyvinyl alcohol having a concentration of greater than percent by weight, adjusting the moisture content .of

the resultant fibers to a value between and percent by weight, stretching said fibers to a ratio of from 1.1 to 3.0 at a temperature of from 0 C. to 100 C., drying such stretched fibers until the moisture content thereof is reduced to a value between 4 and 20 percent by weight, again stretching the said fibers to a ratio of from 2 to 6 at a temperature of less than C., maintaining the said fibers at the constant length and strain imparted thereto by the latter stretch, and thence setting such strain.

2. The process as defined by claim 1, wherein the moisture content of the fibers is adjusted to a value between 80 and 90 percent by weight, the stretched fibers are dried until the moisture content thereof is reduced to a value of about 10 percent by weight, and further wherein the latter stretch is to a ratio of about 4.

3. The process as defined by claim 1, wherein the strain is set by maintaining the said fibers at constant length for at least 24 hours under ambient conditions.

References Cited UNITED STATES PATENTS 2,146,295 2/1939 Herrmann et a1. 264 2,610,359 9/1952 Hatchard et al 2642l0 2,610,360 9/1952 Cline et al 264-210 3,066,999 12/1962 Nakojo et al 264-210 3,238,283 3/1966 Fujii et al 264--210 DONALD J. ARNOLD, Primary Examiner. 

